Low amplitude variability and transient periodicity in FF Andromedae and other active stars

Details Low amplitude variability and transient periodicity in FF Andromedae and other active stars Low amplitude variability and transient periodicity in FF Andromedae and other active stars

Oct 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278..179p&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 1, p. 179-186

Astronomy and Astrophysics

Astrophysics

3

Flare Stars, Stellar Atmospheres, Stellar Spectrophotometry, Variable Stars, Light Curve, Power Spectra, Stellar Flares

Scientific paper

This work presents the first results of a project mainly dedicated to the detection of low amplitude variability in stars with the URSULA double channel photometer fed by the 91 cm telescope of Catania Astrophysical Observatory. URSULA simultaneously observes the target star and a nearby comparison star with two identical photometers and achieves a relative photometric precision down to a few thousandths of magnitude because rapid fluctuations of sky transparency equally affect both stars and are easily removed. We can, therefore, use short integration times and attain high time resolution. The analysis of our observations is based on the methods of periodograms, according to the formulation for unequally spaced time sequences devised by Scargle (1982). We have observed FF And, BY Dra, V 1054 Oph and V 1396 Cyg and detected, at a high level of confidence, several cases of small scale variability, particularly evident in the data of FF And and of V1054 Oph. From FF And we have detected small, but highly significant, dips in the light curve, approximately 25 minutes before a large flare. We compare this finding with the known phenomenology of pre-flare dips and, among other interpretations, we propose them as possible signatures of pre-flare atmospheric activation. We also discuss the data set pertaining to all observed stars.

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